Lagrangian sediment motion in a crescentic nearshore bar under storm-induced waves and currents

Abstract

A fluorescent tracer experiment, in conjunction with morphological and sedimentological data, demonstrates the Lagrangian sediment flux induced by storm waves and currents in a permanently submerged, outer crescentic nearshore bar system. The steady state bar form (height = 2.6 m, wavelength = 390 m) is maintained in the presence of landward sediment advection under asymmetric oscillatory flow during storm buildup and decay and seaward advection under rip-cell flows at the peak of the storm. The seaward displacement of the bar crest in the areas of the convex seaward crescent reflects transport associated with the rip current, which, though variable in its location through time, is never located over the landward projecting horns. The storm studied had a recurrence interval of approximately 1 month and reworked upwards of 16% of the bar sediments. The sediment flux indentified is therefore associated with an event of frequent occurrence and is most likely the control on both bar form and dynamics of the bar system.